Comparative Effectiveness of Mask Type in Preventing SARS-CoV-2 in Health Care Workers: Uncertainty Persists
Authors: Roger Chou
Journal: Annals of Internal Medicine (2022)

EditorialsDecember 2022Comparative Effectiveness of Mask Type in Preventing SARS-CoV-2 in Health Care Workers: Uncertainty PersistsFREERoger Chou, MDRoger Chou, MDOregon Health & Science University, Portland, OregonSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/M22-3219 SectionsAboutVisual AbstractPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail Health care workers have been at the forefront of the COVID-19 pandemic response and are at high risk for acquiring SARS-CoV-2 infection. Infected health care workers can transmit SARS-CoV-2 to coworkers and patients, including persons at risk for severe illness. Therefore, preventing SARS-CoV-2 infection in health care workers is essential to both maintaining an adequate health care workforce and preventing iatrogenic infections.Along with other infection control measures in the hospital setting, personal protective equipment, including masks, is a key component of strategies to prevent SARS-CoV-2 in health care workers. However, the optimal mask type remains uncertain. N95 and equivalent respirators are designed to filter out at least 95% of airborne particles that are 0.3 microns or larger, with minimal leakage when properly fitted (1). By contrast, medical masks filter less efficiently and are loose fitting, enabling leakage, but they are more comfortable, less expensive, do not require fitting, and are more widely available. An ongoing point of contention has centered around when N95 respirators are necessary. Recommendations range from routine N95 use to N95s only for settings in which aerosol-generating procedures are performed (2, 3).Evidence on the comparative effectiveness of different mask types in health care workers has been suboptimal. Until now, the only randomized trials were from the pre-COVID-19 era and indicated similar risk for influenza-like illness with N95 respirators and medical masks (4). Observational studies found that N95 respirators were associated with decreased risk for SARS-CoV-1 infection, but the studies had methodological limitations, including potential recall bias, incomplete SARS-CoV-1 exposure measurement, and residual confounding (5). The applicability to SARS-CoV-2 of observations related to transmission of other viruses is uncertain. Subsequent observational studies in the SARS-CoV-2 era also provided insufficient evidence because of methodological limitations and inconsistent findings (6).Two and a half years after the emergence of the COVID-19 pandemic, Loeb and colleagues (7) report the first randomized trial of N95 respirators versus medical masks in health care workers. This study was designed to determine if medical masks are noninferior to fit-tested N95 respirators for protecting health care workers during routine care of patients with known or suspected COVID-19. Overall, the trial found that the effects of medical masks versus N95 respirators on risk for SARS-CoV-2 infection confirmed by reverse transcriptase polymerase chain reaction were within the predefined noninferiority margin (hazard ratio, 1.14 [95% CI, 0.77 to 1.69]). A slightly higher proportion of participants randomly assigned to N95 respirators reported mask-related adverse events (primarily, discomfort or headaches). Strengths of the trial include the randomized design, pragmatic approach (for example, use of N95 respirators in participants randomly assigned to medical masks permitted when deemed necessary), and high mask type adherence. Despite evidence suggesting that outside exposures may be a stronger risk factor for COVID-19 than work exposures (8), a post hoc analysis found similar findings in participants with or without nonwork exposures.The noninferiority margin used by the trial warrants closer examination. The prespecified noninferiority margin was a 5% absolute increase in COVID-19 incidence confirmed by reverse transcriptase polymerase chain reaction. This was based on preserving an estimated 50% of the observed N95 respirator benefit versus no mask from a prior retrospective study of SARS (9) and the input of health care professionals. Yet, the 5% increase represents a potential doubling of risk with medical masks—a generous noninferiority threshold which may be unacceptable to many health workers. In fact, the finding of noninferiority in this trial was consistent with up to a relative 70% increased risk.The trial protocol also underwent several changes because of the evolution of the pandemic and availability of vaccination. These included expanded eligibility from nurses to any health care worker providing direct patient care, expansion to additional countries, permitting extended and reuse of N95 respirators, reducing follow-up from 12 to 10 weeks, expanding symptomatic criteria for COVID-19 testing, excluding previously vaccinated health care workers, continuing assessment of outcomes for 2 weeks in health care workers vaccinated during the trial, and increased sample size. These changes aimed to enhance enrollment and statistical power, maintain a pragmatic approach, and account for uptake of COVID-19 vaccinations. Although the changes do not seem to have biased findings, use of an adaptive or other flexible design could have better anticipated and addressed modifications to study methods (10).There was substantial heterogeneity in outcomes by country. A post hoc analysis stratified by country reported hazard ratios that ranged from 0.95 in Egypt (where participants were enrolled later in the pandemic and seroprevalence was high) to 2.83 in Canada (where participants were enrolled early in the pandemic and seroprevalence was low). Among the factors that could contribute to this heterogeneity are differences in vaccine types, vaccination rates, infection control measures, local transmission dynamics, and enrollment during periods when different variants were predominantly circulating. This heterogeneity warrants caution in the interpretation of the trial findings. Nearly three quarters (74% [73 of 99]) of cases occurred in Egypt, where medical masks were within the noninferiority margin (hazard ratio, 0.95 [CI, 0.60 to 1.50]). Estimates from other countries did not meet noninferiority criteria but were based on few events (range, 5 to 11) and were very imprecise, with overlapping CIs. Therefore, both the combined and site-specific findings are inconclusive. Yet, the stratified analysis enables one to judge that the trial findings are likely most applicable to an Omicron-predominant, high baseline COVID-19 seroprevalence setting.The trial had other limitations. It was not designed to evaluate the effects of mask types as source control or in effectively vaccinated health care workers. The trial was unable to assess the effect of Omicron or other variants on mask effectiveness. Some subgroup analyses were post hoc, and it was not possible to determine how the findings varied according to factors affecting SARS-CoV-2 transmission, such as ventilation, use of other infection control measures, specific health care setting, or vaccination status.Nonetheless, this trial provides the best evidence to date on comparative effectiveness of mask types in preventing SARS-CoV-2 infection in health care workers providing routine patient care. The results indicate that medical masks may be similar to N95 respirators in Omicron-era settings with high COVID-19 seroprevalence—but would not have met a more stringent noninferiority threshold (for example, 30% relative increased risk). Therefore, the results are not definitive. Decisions about mask types in health care workers should be informed by the uncertainty around the estimates and continue to account for health care worker preferences about potential tradeoffs, N95 respirator availability, and resource constraints.References1. Das S, Sarkar S, Das A, et al. A comprehensive review of various categories of face masks resistant to COVID-19. Clin Epidemiol Glob Health. 2021;12:100835. [PMID: 34368502] doi:10.1016/j.cegh.2021.100835 CrossrefMedlineGoogle Scholar2. World Health Organization. WHO recommendations on mask use by health workers, in light of the Omicron variant of concern: WHO interim guidelines, 22 December 2021. Accessed at www.who.int/publications/i/item/WHO-2019-nCoV-IPC_Masks-Health_Workers-Omicron_variant-2021.1 on 21 October 2022. Google Scholar3. Centers for Disease Control and Prevention. Interim infection prevention and control recommendations for healthcare personnel during the coronavirus disease 2019 (COVID-19) pandemic. Accessed at www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html on 21 October 2022. Google Scholar4. Bartoszko JJ, Farooqi MAM, Alhazzani W, et al. Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: a systematic review and meta-analysis of randomized trials. Influenza Other Respir Viruses. 2020;14:365-73. [PMID: 32246890] doi:10.1111/irv.12745 CrossrefMedlineGoogle Scholar5. Chou R, Dana T, Jungbauer R, et al. Masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings. A living rapid review. Ann Intern Med. 2020;173:542-55. [PMID: 32579379] doi:10.7326/M20-3213 LinkGoogle Scholar6. Chou R, Dana T, Jungbauer R. Update alert 8: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings [Letter]. Ann Intern Med. 2022;175:W108-09. [PMID: 35878407] doi:10.7326/L22-0272 LinkGoogle Scholar7. Loeb M, Bartholomew A, Hashmi M, et al. Medical masks versus N95 respirators for preventing COVID-19 among health care workers. A randomized trial. Ann Intern Med. 2022;175:1629-38. doi:10.7326/M22-1966 LinkGoogle Scholar8. Chou R, Dana T, Buckley DI, et al. Update alert 10: epidemiology of and risk factors for coronavirus infection in health care workers [Letter]. Ann Intern Med. 2022;175:W8-9. [PMID: 34781714] doi:10.7326/M21-4294 LinkGoogle Scholar9. Loeb M, McGeer A, Henry B, et al. SARS among critical care nurses, Toronto. Emerg Infect Dis. 2004;10:251-5. [PMID: 15030692] CrossrefMedlineGoogle Scholar10. Stallard N, Hamborg T, Parsons N, et al. Adaptive designs for confirmatory clinical trials with subgroup selection. J Biopharm Stat. 2014;24:168-87. [PMID: 24392984] doi:10.1080/10543406.2013.857238 CrossrefMedlineGoogle Scholar Comments0 CommentsSign In to Submit A Comment Charles FogartyMedical Director, Spartanburg Medical Research, Spartanburg, SC 293031 December 2022 "Equally effective" establishes equality but not effectiveness. Without data from a placebo arm, it is possible that the infection rate with no mask would have been the same as with a mask. Thus, the equal effectiveness of the two masks could be explained by the possibility that neither mask provided better protection than no mask. KEITH R SCHLESINGEROregon Homecare Commission, USA16 February 2023 Home Care Worker Fogarty's comment implies that mask-wearing is purely performative, and that no prior evidence exists for mask-wearing in a healthcare setting. However imperfect that evidence might be from a formal research "gold standard," to behave as if it simply does not exist in any meaningful form is frankly shocking and in my view professionally disqualifying. Fogarty ought to know that requiring a placebo in a safety study violates ethical standards and rational safety protocols. However, if as director of Spartanburg Medical Research, whose website claims to have, "conducted research trials in Spartanburg for more than 20 years," they can somehow prevail on healthcare professionals in Spartanburg or elsewhere to not wear masks on a randomised basis for the sake of more potent research results, I will certainly pay close attention to outcomes obtained at such heroic risk.Just bear in mind that they would also need to obtain permission from patients and possibly other staff and visitors exposed to the iatrogenic risks imposed on them by healthcare professionals cooperating with such a research protocol. I for one would not agree to participate in this protocol and accept the exposure risks, either as a healthcare worker, support staff, or mere family member or other visitor to the healthcare site. Author, Article, and Disclosure InformationAuthors: Roger Chou, MDAffiliations: Oregon Health & Science University, Portland, OregonDisclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M22-3219.Corresponding Author: Roger Chou, MD, Oregon Health & Science University, Mail Code: BICC, 3181 SW Sam Jackson Park Road, Portland, OR 97239; e-mail, [email protected]edu.This article was published at Annals.org on 29 November 2022. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetailsSee AlsoMedical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Mark Loeb , Amy Bartholomew , Madiha Hashmi , Wadea Tarhuni , Mohamed Hassany , Ilan Youngster , Ranjani Somayaji , Oscar Larios , Joseph Kim , Bayan Missaghi , Joseph V. Vayalumkal , Dominik Mertz , Zain Chagla , Maureen Cividino , Karim Ali , Sarah Mansour , Lana A. Castellucci , Charles Frenette , Leighanne Parkes , Mark Downing , Matthew Muller , Verne Glavin , Jennifer Newton , Ravi Hookoom , Jerome A. Leis , James Kinross , Stephanie Smith , Sayem Borhan , Pardeep Singh , Eleanor Pullenayegum , and John Conly Metrics December 2022Volume 175, Issue 12Page: 1763-1764KeywordsCOVID-19Health care providersInfection controlRespirators ePublished: 29 November 2022 Issue Published: December 2022 Copyright & PermissionsCopyright © 2022 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...